1. Field of the Invention.
This invention relates to methods and apparatus for activating and deactivating pressure responsive downhole equipment and, more particularly, to methods and apparatus for setting and unsetting downhole retrievable inflation packers.
2. Description of the Prior Art.
Packers are widely used in the petroleum recovery industry for sealing against the well bore, the casing I.D. surface, or the O.D. surface of a tubing string. Packers may generally be categorized as either permanent packers or retrievable packers. As its name suggests, a permanent packer is intended to be set in the well and left in place for an indefinite period of time. A retrievable packer, on the other hand, is returned to the surface when its intended function is complete. Retrievable packers frequently must be able to be lowered downhole through a small diameter production tubing string, effectively seal against a large diameter casing, and then be returned to the surface through the tubing string. A retrievable packer is cost effective since the packer may be reused. Moreover, its retrieval to the surface is often critical in order that the packer not interfere with subsequent downhole operations.
Packers may be set or activated by either mechanical or hydraulic forces; the latter type is frequently called an inflation packer. Inflation packers, activated by fluid pressure, have certain advantages over packers activated by mechanically moving parts, including generally increased expansion capability. Thus, an inflation packer is generally preferred when the packer must pass from the surface downhole through a small diameter restriction, be activated or "set" to seal against a much larger diameter casing, and then be deactivated or "unset" and retrieved back to the surface through the small diameter restriction.
Prior art inflation packers are typically set by passing a pressurized fluid from the surface through a tubing string downhole to the packer. The pressurized fluid fills the expandable bladder or bladders of the packer, and pressurizes the bladder with an axially directed force for sealing engagement against the casing. For this reason, an inflatable packer is commonly referred to as a Production Injection Packer, or PIP.
With respect to mechanically activated packers, the packers may be set either by dropping a weight through the production tubing, or by using an explosive pressure setting assembly supported by a wireline. The latter device utilizes the products of combustion to move a slidable piston, which then operates various mechanical components in the packer to set the packer. A significant advantage of a wireline pressure setting device is that the expense of a surface rig or coil tubing mechanism is avoided. The disadvantages, however, of packers set by the movement of mechanical components relate to their generally reduced sealing area compared to inflation packers, and to the difficulty or impossibility of retrieving mechanically set packers through relatively small diameter restrictions.